The goal of this research is to better determine the relations between two classes of adaptation-like effect in the auditory system. The first effect, exemplified by the phenomenon known as overshoot, is typically studied using a wideband masking noise and very brief tonal signals of high frequency. The second effect, called the temporal decline of masking, is typically obtained using longer and lower frequency signals and a masker that does not overlap the signal spectrally. These two effects have always been treated as separate even though they have similar time courses. We have previously shown that there are large, systematic individual differences in the temporal decline of masking and we plan to use these individual differences as a tool for better determining the similarities and differences between overshoot and the temporal decline. Specifically, the plan is to study various other psychoacoustical tasks using subjects have already been dichotomized on the temporal-decline task. To the extent that the subjects dichotomize in the same way on other tasks, information will have been gained about the communality of underlying mechanisms. In the process, we will be able to test directly one popular explanation of the temporal decline--"adaptation" of lateral suppression. A second tool to be used is temporary hearing loss induced by exposure to intense sound or by aspirin use. We have already shown that both these agents reduce or eliminate the overshoot effect, and both of these agents are known to affect the so-called cochlear amplifier. One question to be investigated is whether the temporal decline of masking is similarly affected by exposure-induced and aspirin-induced hearing loss. Also of interest is whether certain, apparently related, psychoacoustical effects (lateral suppression and auditory distortion products) are also affected by these two agents. In the end, more should be known about the common mechanisms underlying a number of auditory skills, and about how those skills are altered by hearing loss. These findings may eventually prove valuable to designers of advanced processing circuitry for hearing aids. The experimental procedures will be the standard ones of modern psychoacoustics. Crews of human listeners will be hired to listen, over earphones, for signals of various sorts embedded in noises of various sorts. Listening sessions will run about 2 hours/day, 5 days/week, for the full semester. For the aspirin experiments, there will be full medical screening and oversight.